diff --git a/db/db_impl.cc b/db/db_impl.cc
index b6fc925..de87e07 100644
--- a/db/db_impl.cc
+++ b/db/db_impl.cc
@@ -605,6 +605,7 @@ void DBImpl::TEST_CompactRange(int level, const Slice* begin,
   assert(level <= config::kNumLevels);
 
   if (level == config::kNumLevels) {
+    // TTL: TODO: update files in the last level
     return;
   }